1. Field of the Invention
The invention relates to a process and a device for measuring the torque of an internal combustion heat engine and, more specifically, to a device for measuring the average gas torque per combustion, produced by such an engine during each combustion, in particular when it is mounted on a passenger vehicle or on a commercial vehicle.
2. Description of the Related Art
In an internal combustion heat engine, the torque produced is the resultant of many parameters and reflects the adequacy of their settings. It constitutes the output of a complex dynamic system. Its measurement is relatively simple and usual on a test-bed, but the cost of this measurement is relatively high. Further, the usual measuring beds deliver only the average values on several combustion cycles of the torque of the engine in stabilized operation. Such measurements of average values over a large number of combustions are insufficient in many respects, for optimizing certain settings of the engine or for diagnosing certain operating defects. Of these defects, detection and statistical evaluation of misfirings are necessitated by new international regulations.
To achieve the above objectives, the quantitative analysis of the average gas torque per combustion produced by the combustions of the gas mixture in the various cylinders of the heat engines is necessary. Such an analysis so far has been made only in the laboratory or on very high-power engines, and it generally relies on increases of pressure in the combustion chambers. This technique exhibits the major drawback of being able to be used only on engines designed (or specially modified) to make possible an installation of pressure sensors. In addition, it obviously is not immediately applicable to engines routinely mounted on a vehicle and, further, it remains so as long as the reliability, the cost, the life and the convenience of use of the pressure sensors are not in accordance with the economic requirements of the automobile industry.
In a PCT international patent application, filed by Motorola Inc. and published on Jun. 20, 1990 under No. WO 90/07051, an electronic control system of the operation of an internal combustion heat engine is described. This system is based on the concept that the instantaneous value of the advancement period of the teeth of a measuring ring gear, integral with the inertial flywheel of the engine, and in front of a stationary sensor, corresponds to the measurement of the instantaneous power output successively produced in each of the cylinders of the engine. The signal thus produced by the sensor is accordingly processed. This processing consists in: (1) measuring the instantaneous period d.sub.i for advancement of a tooth of the ring gear in front of the sensor, (2) respectively multiplying periods d.sub.i of the teeth relating to each of the cylinders by given weighting factors P.sub.i belonging to a sequence corresponding to a particular operating criterion of the engine such as pinging or power output (the procedure for determining these factors is not described), (3) adding results d.sub.i .multidot.P.sub.i obtained for each cylinder, (4) comparing this sum to a particular value taken as reference, (5) deducing, if necessary, from the result of this comparison the presence of pinging in a cylinder or a power imbalance of a cylinder relative to the others and (6) consequently modifying the supplying of the cylinder with an air-fuel mixture.
The object of the system thus described is to eliminate all pinging in the cylinders of the engine and/or to balance the instantaneous power outputs provided by each of them. As a result, the absolute value of the various intermediate magnitudes obtained is neither desired nor found.